Crossed Dragone

The Crossed Dragone Telescope is an off-axis telescope design consisting of a parabolic primary mirror and a large concave secondary mirror arranged so that the focal plane is at right angles to the incoming light.

At millimeter and submillimeter wavelengths this greatly decreases systematic effects due to diffraction.

Some examples of existing and planned telescopes that use this design include: Although the field of view of Crossed Dragone telescope is large, it can be increased further by the addition of canceling aspheric terms in the primary and secondary mirror shapes.

This comes at the cost of breaking the symmetry of the mirrors – they are no longer rotationally symmetric around any axis.

Modern machining techniques can cut such surfaces but on a large telescope the mirror will be made of many segments/panels.

A cross section of a ray trace through a Crossed Dragone telescope. The primary mirror is on the bottom, the secondary on the left and the focal plane on the right.